Debt - Additional Information (Details)		3 Months Ended	6 Months Ended
	Nov. 11, 2019 USD ($) tranche	Jun. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Nov. 25, 2019 USD ($)
Line of Credit Facility [Line Items]
Term loan, net of facility fees, lender expenses and issuance costs		$ 76,338,000	$ 76,338,000
Derivative liability		1,890,000	1,890,000	$ 1,650,000
Collateral Agent, Pharmakon
Line of Credit Facility [Line Items]
Derivative liability		1,900,000	$ 1,900,000	$ 1,700,000
Biopharma Credit Investments V (Master) LP | Keryx | Term Loan | Collateral Agent, Pharmakon
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 100,000,000.0
Line of credit, maximum borrowing capacity, number of available tranches | tranche	2
Term loan, maturity date, description	The Term Loans will mature on the fifth anniversary of the Tranche A Funding Date, or the Maturity Date.
Term loan, maturity term	5 years
Term loan payment description			The Company will repay the principal under the Term Loans in equal quarterly payments starting on the 33rd-month anniversary of the applicable Funding Date or, if certain conditions are met, it will have the option to repay the principal in equal quarterly payments starting on the 48th-month anniversary of the applicable Funding Date, or collectively the Amortization Schedule. Under certain circumstances, unless certain liquidity conditions are met, the Maturity Date may decrease by up to one year, and the Amortization Schedule may correspondingly commence up to one year earlier
Term loan, maturity term, potential reduction (up to)	1 year
Term loan, amortization period, potential reduction (up to)	1 year
Facility fee percentage on principal amount	2.00%
Facility fee paid, amount	$ 2,000,000.0
Prepayment premium percentage on principal if prepaid prior to third anniversary of funding	2.00%
Prepayment premium percentage on principal if prepaid prior to fourth anniversary and after third anniversary of funding	1.00%
Prepayment premium percentage on principal if prepaid after fourth anniversary of funding	0.50%
Interest expense		$ 2,200,000	$ 4,400,000
Biopharma Credit Investments V (Master) LP | Keryx | Term Loan | Collateral Agent, Pharmakon | Three-month LIBOR
Line of Credit Facility [Line Items]
Basis spread on floating interest rate	7.50%
Biopharma Credit Investments V (Master) LP | Keryx | Term Loan | Collateral Agent, Pharmakon | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, floor rate	2.00%
Debt instrument, cap rate	3.35%
Biopharma Credit Investments V (Master) LP | Keryx | Term Loan | Collateral Agent, Pharmakon | Tranche A
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 80,000,000.0
Amount drawn under credit facility, date			Nov. 25, 2019
Term loan, net of facility fees, lender expenses and issuance costs					$ 77,300,000
Biopharma Credit Investments V (Master) LP | Keryx | Term Loan | Collateral Agent, Pharmakon | Tranche B
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 20,000,000.0
Last date to draw amount under credit facility			Dec. 31, 2020